At least four people have died and 49 are still missing after an oil rig overturned in the Sea of Okhotsk in the Russian Far East, the regional emergencies service reported on Sunday.
The Kolskaya drilling rig with 67 people aboard was being towed in a severe storm, when it overturned and sank some 200 km (125 miles) off Russia's Sakhalin Island early on Sunday.
Fourteen people have been rescued, the emergencies service said.
Russia's Transport Ministry told Prime news agency that "of the 67 people aboard the Kolskaya rig, 53 are crewmembers and 14 are workers and support staff."
The drilling rig belongs to the Arktikmorneftegazrazvedka exploration company, which carried out work under a contract with energy giant Gazprom.
The drilling rig, which can take up to 102 people on board, was built in 1985 in Finland. The rig started its operations in September to drill and test the Pervoocherednaya well on the West-Kamchatka licensed block of the Okhotsk Sea shelf.
The rig, which is 69 meters long and 80 meters wide, was intended to drill a well at a depth of 3,500 meters.
A Gazprom spokesman said that the rig had fulfilled its works for Gazprom by the time of the accident and was heading for its base.
Investigators have said they are considering the rig's tow in disregard of a severe storm as the most likely reason for the accident.
The regional emergencies service has said the accident poses no threat to the environment.
"Fuel stocks at the Kolskaya drilling rig are minimal and are stored in hermetically sealed tanks, and there is no danger of a fuel spill," the service said.